Some filenames satisfy particular naming protocols. For example, suppose that a user on a computer running a Unix® operating system accesses a particular text file by referring to the string “root/user/TextFileInTheUserDirectory.txt”. In this case, the filename “TextFileInTheUserDirectory.txt” satisfies a Unix naming protocol that requires, for example, a 255-byte limit to filename length with case sensitivity. Other naming protocols include the Microsoft® Windows, or M256, naming protocol having a limit of 255 case insensitive Unicode characters in filename length with a list of reserved characters, and the DOS, or M83, naming protocol having a filename limit of twelve case-insensitive characters, with 8 characters for a base name, 3 characters reserved for an extension, and a “.” separating the base name and the extension. (In other words, a DOS filename takes the form “xxxxxxxx.yyy,” where the x's and y's represent ASCII characters.)
Some directories are multiprotocol in that they support multiple naming protocols. That is, a multiprotocol directory supports access to a single file by users on computers running different operating systems, each of which supports different naming protocols. For example, a first user on a computer running Unix and a second user on a computer running Windows may both be able to access the single file. Along these lines, the directory maps each of these filenames to the same inode number.
In response to the naming of a file in one naming protocol, a file system containing a multiprotocol directory may create equivalent filenames in each of the other naming protocols it supports. Along these lines, suppose that a user creates the following filename for a file on a computer running Windows: “TextFileInTheUserDirectory.txt”. The computer would then translate this name into, say, Unix and DOS according to the rules governing the respective naming protocols. In a conventional naming process, the conversion from a longer M256 or Unix filename to a shorter M83 filename involves truncating the longer filename to at most eight characters, such as in “TEXTFI˜1.TXT”. Other rules govern M256 filenames that have characters reserved in DOS.